Since 2001, the Utah Pediatric Heart Network's accomplishments in performing clinical research, including protocol design, recruitment, study performance, data analysis and interpretation, and dissemination of results, demonstrate their willingness to collaborate with the other clinical centers, the Data Coordinating Center, and NHLBI. This study addresses the significant problem of growth failure in infants with hypoplastic left heart syndrome (HLHS). As the first study to evaluate the effectiveness of a pharmacologic intervention that does not target the cardiovascular system to improve growth, it also demonstrates innovation. The improved survival of infants with HLHS is accompanied by considerable morbidity and resource utilization. Their hospital costs are among the highest of any type of birth defect, exceeding $180,000,000/year. Infants with HLHS undergo at least two complex palliative procedures during their first few months: aortic arch reconstruction with pulmonary artery shunt (Norwood procedure) often before one week of age, and superior cavopulmonary connection (SCPC) usually at four to six months of age. Neonatal cardiac surgery places a significant metabolic stress on these infants, many who are already malnourished at the time of their operation. After the Norwood procedure, infants have a drastic decline in weight for age and continue to grow poorly between Nonwood discharge and the SCPC surgery. Poor growth is one of the most important risk factors for prolonged hospitalization, death or transplant, and impaired neurodevelopment. Medications aimed at improving hemodynamics and specific feeding protocols have failed to improve growth in these infants. Oxandrolone is an anabolic steroid that has been in routine clinical use for over 30 years. The drug has few side effects and has improved weight gain in children with extensive burns and improved growth in children with short stature, including girls with Turner's syndrome. We propose a multicenter, randomized, double- blind, placebo-controlled trial to assess the impact of a short course (30 days) of oxandrolone therapy to promote growth in infants with HLHS. The specific aims are to: 1) evaluate the effectiveness of oxandrolone therapy on growth, hospital course, and neurodevelopmental outcome and 2) describe the safety profile of oxandrolone therapy in infants with HLHS. RELEVANCE: Surviving infants with HLHS have ongoing medical problems and high health care costs. These infants grow poorly in the first months of life, increasing their risk for longer hospitalizations, poor neurodevelopment, and heart transplant or death. Growth is not improved by medications aimed at improving hemodynamics or by specific feeding methods. Oxandrolone is a drug that has helped other children gain weight If successful, oxandrolone therapy would represent a major breakthrough impacting the field by improving outcomes and decreasing the resource utilization for infants with HLHS.